cells separating the dead mass from the green peripheral cells was 

 always from one to four greater within the cast than above or 

 below it. 



Another leaf from which the cast was removed after an appli- 

 cation of 18 days showed no infolding, yet all peripheral cells had 

 greatly elongated toward the centre and some of the weak cells there 

 were crowded together. Except these few collapsed ones all of the 

 central , hyaline cells , 6 to 8 in a radius were living , while above 

 and below the cast were but one or two rows of similar cells. 



Two casts were now applied in a manner different from the 

 preceding, the first to compel less longitudinal growth within the 

 cast, the second to check growth at an earlier stage than had been 

 done. For the first purpose, the leaf was made to take a zigzag course 

 through the cast by thrusting pins through the paper mould before 

 the gypsum was poured in and thus bending the leaf back and forth. 

 For the second experiment, the scales of an onion were so cut away 

 above that a cast could be applied 2 cm lower than previously done. 

 The first cast remained 13 days, the second 15 days, the leaves in 

 question carrying the cast up from the bulb and attaining in this 

 period each a length of 15 cm . This time was taken to end the ex- 

 periments since the leaves then showed the beginning of the infold- 

 ing at the upper limit of the cast. 



Removal of the casts and sectioning showed in each leaf a solid 

 mass of living tissue, — no dead cells anywhere. The central mass 

 of parenchyma cells did not show the spongy condition which it had 

 when the casts were applied. The cells had been crowded closely 

 together by growth toward the centre. Above and below the casts 

 the leaves had their normal cavities. 



The changes in tissue or cells induced by the casts were marked 

 everywhere by the incomplete development of the assimilating cells, 

 and by the abnormal radial elongation of the 2 inner rows of the 

 same tissue. In the normal the mechanical tissue is but slight and 

 no change was here evident within the casts. 



Equisetum limosum L. 



In addition to what Frank 1 has written on the formation of the 

 intercarinal canals in Equisetum, a few words may be given as to 

 the time of this formation. 



Beitrage zur Pflanzenphysiologie. Leipzig 1868. 



